There's very little on these engines that ISN'T sourced from GM and the coils are the same as what comes on Northstar engines. The ECM can be bought from other sources, too. The dealer should have shipped the ECM to Indmar or MC for testing, rather than just replacing it.

I haven't bought the coil or ECM yet so I am definitely interested in GM sourced parts. Any idea on how to identify the GM numbers for the LTR? I want to try your idea and replace that 1/4 coil pack because I think that will solve it. Maybe I can avoid the ECM altogether.